Mechanical and chemical-mechanical planarization processes (collectively “CMP”) remove material from the surface of micro-device workpieces in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a carrier head 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 between an upper surface 22 of the platen 20 and a lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F) and/or reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The carrier head 30 has a lower surface 32 to which a micro-device workpiece 12 may be attached, or the workpiece 12 may be attached to a resilient pad 34 under the lower surface 32. The carrier head 30 may be a weighted, free-floating wafer carrier, or an actuator assembly 36 may be attached to the carrier head 30 to impart rotational motion to the micro-device workpiece 12 (indicated by arrow J) and/or reciprocate the workpiece 12 back and forth (indicated by arrow l).
The planarizing pad 40 and a planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the micro-device workpiece 12. The planarizing solution 44 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the micro-device workpiece 12, or the planarizing solution 44 may be a “clean” non-abrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and clean non-abrasive solutions without abrasive particles are used on fixed-abrasive polishing pads.
To planarize the micro-device workpiece 12 with the CMP machine 10, the carrier head 30 presses the workpiece 12 face-downward against the planarizing pad 40. More specifically, the carrier head 30 generally presses the micro-device workpiece 12 against the planarizing solution 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier head 30 moves to rub the workpiece 12 against the planarizing surface 42. As the micro-device workpiece 12 rubs against the planarizing surface 42, the planarizing medium removes material from the face of the workpiece 12. The force generated by friction between the micro-device workpiece 12 and the planarizing pad 40 will, at any given instant, be exerted across the surface of the workpiece 12 primarily in the direction of the relative movement between the workpiece 12 and the planarizing pad 40. A retaining ring 33 can be used to counter this force and hold the micro-device workpiece 12 in position. The frictional force drives the micro-device workpiece 12 against the retaining ring 33, which exerts a counterbalancing force to maintain the workpiece 12 in position.
The planarity of the finished micro-device workpiece surface is a function of the distribution of planarizing solution 44 under the workpiece 12 during planarization and several other factors. The distribution of planarizing solution 44 is a controlling factor for the distribution of abrasive particles and chemicals under the workpiece 12, as well as a factor affecting the temperature distribution across the workpiece 12. In certain applications it is difficult to control the distribution of planarizing solution 44 under the micro-device workpiece 12 because the retaining ring 33 wipes some of the solution 44 off of the planarizing pad 40. Moreover, the retaining ring 33 can prevent proper exhaustion of the planarizing solution 44 from inside the retaining ring 33, causing a build-up of the planarizing solution 44 proximate to the trailing edge. These problems cause an uneven distribution of abrasive particles and chemicals under the micro-device workpiece that results in non-uniform and uncontrollable polishing rates across the workpiece. To solve this problem, some retaining rings have grooves. These retaining rings, however, have not been very effective at exhausting the planarizing solution.
FIG. 2 schematically illustrates another rotary CMP machine 110 with a first platen 120a, a second platen 120b, a first carrier head 130a, and a second carrier head 130b. On the CMP machine 110, the first carrier head 130a rotates in a first direction D1, and the second carrier head 130b rotates in a second direction D2. Because the carrier heads 130a-b rotate in different directions, retaining rings with different grooves are used for each carrier head 130a-b. The use of two different retaining rings increases inventory costs and can result in the wrong ring being placed on a carrier head 130.